In populated areas of developed parts of the world access to communication networks is readily available. Communication networks that are available include cellular data and telephony networks, broadband cable and fiber optic networks, for example. However outside of populated areas of the developed world terrestrial communication networks may be absent. For these areas, satellite communication networks provide a valuable means of communication. For example, satellite communication networks may be used by scientists and engineers engaged in field work or by military units. Additionally there are machine-to-machine applications in which machinery located at remote sites can be provided with satellite connectivity so that the operation of the machinery can be automatically reported to a central operations site.
Satellite communication systems can be classified by the distance of their satellites' orbit from earth, which are put into three categories geosynchronous (35,786 km from the earth surface), Medium Earth Orbit (MEO, above 2000 km but below 35,786 km), and Low Earth Orbit (LEO, above 160 km but below 2000 km). Satellite systems with LEO satellites offer the advantage that the transmit power required to achieve a given bit rate is lower than it would be for geosynchronous and MEO satellites.
A directional antenna because of its higher gain has the potential to increase the achievable bit rate because it improves the link budget. However an issue with LEO satellites is that they relatively rapidly traverse from horizon to horizon and therefore a directional antenna would need to be constantly changing pointing direction while in operation. A mechanical tracking system would need to be relatively expensively made to handle the constant satellite tracking for the expected lifetime of the antenna which might be 10,000 hours.
Another issue with LEO communication systems is that the distance to the satellite varies significantly as it traverses from horizon to horizon and therefore the signal spreading losses also vary significantly, being much higher when the satellite is located closer to the horizon at high zenith (co-latitude) angles relative to the earth station. Certain LEO communication satellite systems partly compensate for this by aiming the maxima of their gain patterns at a high zenith angle, however the compensation is only partial.
What is needed is an antenna for LEO satellite communication systems that exhibits high gain, particularly at high zenith angles, and is able to track LEO satellites.